The present invention relates to a method and a system for controlling active suspensions of a vehicle.
A known active suspension system of a vehicle comprises suspensions into and out of which fluid is charged and discharged independently to maintain a reference vehicle height by extending and contracting the suspensions responsive to vertical relative displacements between the wheels and the vehicle body at the positions of the respective suspensions.
Japanese Patent Application Laid-Open Pub. No. 2-95,911 discloses an active suspension system as described above wherein there are provided a longitudinal G-sensor for detecting longitudinal acceleration and a lateral G-sensor for detecting lateral acceleration applied to the vehicle. In the system, pitching and rolling motions of the vehicle are preestimated responsive to the longitudinal and lateral accelerations detected during acceleration, deceleration and turning of the vehicle. The preestimation is performed by charging and discharging quantities of the fluid into and out of the respective suspensions to suppress pitching and rolling of the vehicle.
The active suspension system described above has a feed back control system for controlling the suspensions so as to maintain a reference vehicle height responsive to relative vertical displacements between the respective wheels and the vehicle body. The active suspension system has, in addition to the feed back control system, a feed forward control system for maintaining preestimated vehicle rolling and pitching responsive to longitudinal and lateral accelerations detected during vehicle acceleration, deceleration and turning. By combining the feed forward control system with the feed back control system, the attitude of the vehicle is maintained at a desired attitude without delay.
However, the known active suspension system described above has a disadvantage in that in the case of abrupt braking the driver is caused to feel an unnatural feeling or sensation of being pressed from the forward side because the front part of the vehicle is not lowered even in the event of abrupt braking.